• Tom Lane's avatar
    Improve contrib/pg_stat_statements' handling of garbage collection failure. · 8bbe4cbd
    Tom Lane authored
    If we can't read the query texts file (whether because out-of-memory, or
    for some other reason), give up and reset the file to empty, discarding all
    stored query texts, though not the statistics per se.  We used to leave
    things alone and hope for better luck next time, but the problem is that
    the file is only going to get bigger and even harder to slurp into memory.
    Better to do something that will get us out of trouble.
    
    Likewise reset the file to empty for any other failure within gc_qtexts().
    The previous behavior after a write error was to discard query texts but
    not do anything to truncate the file, which is just weird.
    
    Also, increase the maximum supported file size from MaxAllocSize to
    MaxAllocHugeSize; this makes it more likely we'll be able to do a garbage
    collection successfully.
    
    Also, fix recalculation of mean_query_len within entry_dealloc() to match
    the calculation in gc_qtexts().  The previous coding overlooked the
    possibility of dropped texts (query_len == -1) and would underestimate the
    mean of the remaining entries in such cases, thus possibly causing excess
    garbage collection cycles.
    
    In passing, add some errdetail to the log entry that complains about
    insufficient memory to read the query texts file, which after all was
    Jim Nasby's original complaint.
    
    Back-patch to 9.4 where the current handling of query texts was
    introduced.
    
    Peter Geoghegan, rather editorialized upon by me
    8bbe4cbd
pg_stat_statements.c 85.4 KB